A prospective phase II study was conducted to define the analgesic efficacy, acceptability and toxicity of the transdermal therapeutic system (TTS) of fentanyl in Chinese patients with severe cancer-related pain. A total of 14 patients was treated with TTS fentanyl at doses ranging from 25 to 100 micrograms h-1; initial doses were chosen according to their previous opioid requirement. Standard supportive therapy was given as required. A brief pain inventory (using a 10-point scale) was used to assess patients at days 0, 7 and 14. Pain control on day 14 with TTS fentanyl was successful in six patients, with a reduction in the common side-effects of other opioids and improvement in general well-being. Seven patients did not complete the 14-day trial: two developed dizziness and nausea within 3 h of application; and in five, TTS fentanyl was insufficiently flexible to control increasing pain during the first week. TTS fentanyl was effective and well tolerated in 43% of patients. Acute dizziness and nausea within the first few hours after application and the relative inflexibility of dose-adjustment both limited the use of TTS fentanyl.